1. Field of the Invention
The present invention relates to an expandable stent.
2. Description of the Prior Art
Stents are generally known. Indeed, the term “stent” has been used interchangeably with terms such as “intraluminal vascular graft” and “expansible prosthesis”. As used throughout this specification the term “stent” is intended to have a broad meaning and encompasses any expandable prosthetic device for implantation in a body passageway (e.g., a lumen or artery).
In the late 1980's, the use of stents attracted an increasing amount of attention due the potential of these devices to be used, in certain cases, as an alternative to surgery. Generally, a stent is used to obtain and maintain the patency of the body passageway while maintaining the integrity of the passageway. As used in this specification, the term “body passageway” is intended to have a broad meaning and encompasses any duct (e.g. natural or iatrogenic) within the human body and can include a member selected from the group comprising: blood vessels, respiratory ducts, gastrointestinal ducts and the like.
First generation stents were self-expanding, spring-like devices which were inserted in the body passageway in a contracted state. When released, the stent would automatically expand and increase to a final diameter dependent on the size of the stent and the elasticity of the body passageway. An example of such a stent is known in the art as the Wallstent™.
The self-expanding stents were found by some investigators to be deficient since, when deployed, they could place undue, permanent stress on the walls of the body passageway. Further, upon expansion, the stent would shorten in length in an unpredictable fashion thereby reducing the reliability of the stent. This led to the development of various stents which were controllably expandable at the target body passageway so that only sufficient force to maintain the patency of the body passageway was applied in expanding the stent—i.e., the so-called “balloon expandable stents”.
Generally, in these second generation systems, a stent, in association with a balloon, is delivered to the target area of the body passageway by a catheter system. Once the stent has been properly located (for example, for intravascular implantation the target area of the vessel can be filled with a contrast medium to facilitate visualization during fluoroscopy), the balloon is expanded, thereby expanding the stent by plastic deformation so that the latter is urged in place against the body passageway. As indicated above, the amount of force applied is at least that necessary to maintain the patency of the body passageway. At this point, the balloon is deflated and withdrawn within the catheter, and subsequently removed. Ideally, the stent will remain in place and maintain the target area of the body passageway substantially free of blockage (or narrowing).
A balloon-expandable stent which gained some notoriety in the art in the 1990's was known as the Palmaz-Schatz™ stent. This stent is discussed in a number of patents including U.S. Pat. Nos. 4,733,665, 4,739,762, 5,102,417 and 5,316,023.
Another stent which has gained some notoriety in the art in the 1990's was known as the Gianturco-Roubin Flex-Stent. This stent is discussed in a number of patents, including U.S. Pat. Nos. 4,800,882, 4,907,336 and 5,041,126.
Other types of stents are disclosed in the following patents:
U.S. Pat. No. 5,035,706 (Gianturco et al.),
U.S. Pat. No. 5,037,392 (Hillstead),
U.S. Pat. No. 5,147,385 (Beck et al.),
U.S. Pat. No. 5,282,824 (Gianturco),
Canadian patent 1,239,755 (Wallsten), and
Canadian patent 1,245,527 (Gianturco et al.).
While these prior art stents have achieved a varying degree of success, the art is constantly in need of new stents having improved flexibility and stability while being able to be readily implanted with little or no trauma to the target lumen. It would be highly desirably if such new stents additionally were relatively resistant to kinking during bending while maintaining wall apposition and side branch access (particularly important when deploying the stent in the aorta).